Method and apparatus for bending sheet material



May 6, 1947, R. M. BOEHM ET AL 2,420,119

METHOD AND APPARATUS FOR BENDING' SHEET MATERI'AL 4 Smets-sheet 1 FiledNov. 29, 1944 INVENTOR Fase-fr M 5v5/m4 ,4f/Pou 6l F100/v BY MATTO EYMay 6, 1947- R. M. BOEHM ET Al.' 2,420,119

METHOD AND `AP.Pl-RIFUS FOR BENDING' SHEET MATERIAL I l Filed Nov. 29,1944 4 sheets-sheep 2 .gsi

INVENTOR fPaaE/Pr M 50E/m4 675km/ A A4004/ y ATTORNEY May 6 1947-' R. M.BOEHM ET AL 2,420,119

METHOD AND APPARATUS FOR BENDING SHEET MATERIAL Filed Nov. 29, 1944 4sheets-sheet s AT ORNEY May', 1947- R. M. BOEHM ET AL 2,420,119

METHOD AND APPARATUS FOR BENDING SHEET MATERIAL Filed Nov. 29, 1944 4Sheets-Sheet 4 Patented May 6, 1947 ZAZMIQ METHOD AND APPARATUS FORBENDING SHEET MATERIAL Robert M. Boehm, Laurel, Miss., and Aaron A.Ladon, Cleveland, Ohio, assignors to Masonite Corporation, Laurel,Miss., acorporation of Delaware Application November 29, 1944, SerialNo. 565,768

11 Claims.

This invention relates to a method and apparatus for bending sheetmaterial. It relates especially to a method and apparatus for bendinghardboard sheet material into substantially U-shaped or trough-likearticles which are substantially free from cracking or breaking. By useof the invention the sheet material is held under restraint byapplication of inwardly-directed pressure to its edges throughout thegreater part of the bending operation, and is automatically releasedfrom such restraint when the bending operation is substantiallycompleted.

While the method and apparatus of the present invention may be used toform permanent bends and deformations, substantially without breaking,in materials such as plywood, insulation board, hardboard and the like,the description below will be directed to forming elongated trough-likearticles from plane sheets of lignocellulose liber hardboard. Suchhardboard sheets are conveniently prepared by treatment of wood chipswith steam followed by explosive disruption into fiber substantially asdescribed in U. S. patent to Mason 1,824,221, and the resulting liberrefined, and after its contents of water solubles have preferably beenreduced as by washing, formed into porous sheets containing about 2% to3% sizing material, and then pressed into hardboard sheets under heatand high pressure.

Hardboard sheet materials have heretofore been bent into various shapes,but such operations have generally been limited to bends having arelatively large radius of curvature- In cases where making bends ofrelatively small radius of curvature was atempted, difficulty wasencountered in that the sheet would tend to crack or break.

With the use of the present method and apparatus, the sheet is heldunder edge restraint through substantially the greater part of thebending operation, that is, at least through the critical range of thebending operation wherein cracking and breaking might occur. In bendingsheets While they are so restrained by suitable means applied to theirside edges, the bending will progress by compression of the innersurface rather than by stretching of the outer surface of the sheet andthus cracking or breaking of the sheet will be avoided. Bends ofrelatively small radius may be obtained in this Way without breaking orsurface cracking of the sheet material. When the bending has beencompleted, the edge restraint is automatically released, permitting thebent product to be removed.

An object of the present invention is the pro- 2 vision of a method andan apparatus for producing bends in sheet material, wherein the sheet isheld in restraint throughout substantially the greater part of thebending operation by inward pressure applied to its edges and thenautomatically released from such restraint When the bend has beenformed.

A further object is the provision of a method and apparatus forprcducing bends of relatively small curvature in sheet material withoutcracking or breaking the sheet.

Additional objects and advantages will be clear to those skilled in theart on consideration of the attached description and drawings.

The method of this invention may be performed with various types ofapparatus, and such apparatus may be modied to bend hardboard sheetsinto many forms and shapes. The accompanying drawings illustrate onetype of apparatus which is suitably designed to form troughlike articlesfrom hardboard sheets in accordance with the method described herein.

In such drawings,

Fig 1 is an end view of the apparatus with portions broken away, andshows the sheet to be bent in restrained position prior to the bendingthereof. f

Fig. 2 is a sectional plan View on line 2--2 with portions broken awayof Fig. 1.

Fig. 3 is a sectional end vieW on line 3-3 with portions broken away ofFig, 1.

Figs. 4, 5, and 6 are diagrammatic views illustrating various positionsof different parts of the bending apparatus in relation to the moldduring the bending cycle; and

Fig. 7 is a diagrammatic View illustrating the method for determiningthe locus about which the restraining arm moves.

The illustrated apparatus consists essentially of a heated, preferablyhollow mold, means for holding a hardboard sheet on said heated mold,

restraining means pivoted at points so located that said means will holdthe sheet in restraint by its edges during the principal part of thebending operation and automatically release the sheet during the latterpart thereof, and means to apply a deforming force to the upper surfacesof the sheet to bend the sheet. One of the essential features of theinvention consists in the prevention or minimizing of cracking andbreakage caused by bending by the provision of restraining meansoperating as above described.

This novel feature of restraining the sheet while Y performing most orall of the bending operation and then automatically releasing thepressure on the sheet is accomplished by coaction between the edges ofthe sheet being bent with restraining means which are mounted onswinging arms pivoted to turn about a predetermined point on theapparatus, which point is generally below the horizontal plane of thesheet as originally inserted in place therein, preferably below theupper surface of the moldand adjacent to the curvature of the mold overwhich the sheet will be bent. A mode of determining the location of suchpoints will be described below.

In the drawings, which disclose a suitable ap paratus to form bends inhardlooard sheets, ref'- erence numerals Ill indicate four uprightframemembers rigidly secured in position by transverse cross members l2,I4, and I6 and longitudinally extending members i8, 20, 22.

At a convenient working-level height, a hollow metallic mold 24, whichhas a preferably flat upper surface and downwardly curved spaced sideportions, is mounted onA bed plate 26 and supported by members i8, asshown in Fig. 1. Such a mold is suitable for bending sheet material intosubstantially U-shaped or trough-like articles. Suitable heatingelements 28, such as electrical units, are mounted on the interiorsurface of mold 24 to supply necessary heat to the mold.

Near the upper surface of mold 24 and adjacent to mold curvature 3Dabout which the bend will be formed, a pair of swinging arms 32 aremounted at each side of the mold through pivotal connections 34 onsupporting plates 36. A pair of adjustable sheet-restraining members 38,having angular recessed edges 39, are attached to arms 32 near the outerextremities thereof and extend in substantially parallel alignment withmold 24, there being one of the restraining members 38 along each sideof mold 24. Members 38 serve to apply inwardly directed restrainingpressure to the opposite edges of the sheetY material received inrecesses 39 formed in said members 38. The members 38 may be adjusted tovarious positions on the arms 32 by means of adjusting nuts 40 and 4l,and by this adjustability thel machine is adapted for bending sheetmaterials of different widths. Suitable counterweights 42 are connectedwith restraining members 33 by means of flexible cables 43 which extendover pulleys 43a, and are anchored to eyes 43D on the restrainingmembers' 38. The counterweight arrangement serves to substantiallybalance the weight of the arms 32 and restraining members 38 as shown inFig.V l.

A hold-down plate 44, provided with an angular ange 46, is movablypositioned above mold 24 and is adapted, when in the lowered position,to rmly clamp the sheet between it and the upper surface of mold 24. Aseries of movable linkages 48-50, 49--5I, and 52-54 are provided to linkflange 46 of plate 44 to frame member 22 through a toggle-jointarrangement. A manually-operated lever 58, pivotally mounted on framebracket 60, imparts movement to the toggle-joint arrangement throughangular link 56 and a movable connection at 62, thereby moving hold-downplate 44 toward and away from the upper surface of mold 24. Linkages 48and 50 are connected by cross link 64 to impart uniform movement toplate 44 at all times. Spring 66 fastened to link and frame bracket 68serves to prevent excessive side movement of plate 44 when thetoggle-joint arrangement is operated.

The pressure-applying means used for eiecting the bending consists of apair of spaced rolls and 12 extending in substantially parallelalignment with mold 24 and movably positioned above the curved portions30 of the mold. Rolls 1G and 12 are rotatably mounted at the lowerextremities of bars 14 and 16 and spaced from each other by slottedconnecting member 18. The sloted portion of member 18 permits relativelateral movement of rolls 10 and 12 during their downward movement inthe bending operation. Springs 86 tend to pull rolls 10 and 12 towardeach other at all times. The upper extremities of bars 14 and 16 arepivotally connected at 82 to channel member 84 which is verticallymovablel and serves as a common supporting member for the pressureapplying means. Racks 86, operating in guiding channels 83, positionedat each end of the machine, are connected to member 84. Drive pinions93, mounted on shaft 92, which is supported by shaft bearings 93,intermesh with the teeth on racks 86, and, as pinons 90 are rotated, asubstantially vertical movement of the mechanism attached to channelmember 84 may be obtained. Rotative movement is transmitted to pinions9e through pulley 94 mounted on shaft 92 and driven by any suitabledriving means (not shown).

In using the apparatus for bending sheet material, the pressure-applyingmechanism and the clamp plate 44 are first raised to their respectiveuppermost positions. When the parts referred to are thus positioned,sufficient clearance is provided between tlie mold and the raised partsfor easy positioning of sheet material 96 on top of mold 24. Inpositioning sheet 96, preparatory to the bending operation, the sideportions of the sheet extend outwardly beyond the curved sides of themold, and the edges of the extended portion are placed in the recesses39 formed in restraining bars 38. The bars 38 are preferably so adjustedby nuts 4U, 4I that it will be necessary to slightly flex the sheet inorder to insert the edges thereof in recesses 39 of the restraining bars38 in a manner which will give a tight fit between the edges of thesheet and the restraining bars.

Such sheets are preferably treated with water before the bendingoperation for easier bending of the sheet, although such a step is notnecessary in allrcases. In many cases sheet materials have asufliciently high moisture content to make dampening with waterunnecessary.

When sheet material S6 has been placed on the top surface of heated mold24 as described,

hold-down clamp 44 is lowered into contact with the sheet, thus rmlyholding the sheet between the upper surface of mold 24 and clamp 44.Rolls 10 and 12 are now lowered by means of racks 83. As the rolls 13and 12 make contact with the sheet 96 and their downward movementcontinues, downward pressure is thereby applied in substantiallyvertical planes to the upper surface of the extended side portions ofsheet 93. Thus the side portions of the sheet extending out beyond mold24 will be forced inwardly toward the side-forming portions of mold 24.By bending in this way the sheet will be shaped to the curvature of themold.

Upon the application of downward pressure to the surface of the sheet,restraining bars 38 are moved downward with and preferably by theextending side portions of the sheet to describe an arcuate path aboutpivot points 34 as the sheet material is gradually forced toward thesides of the mold. Near the end of the bending operation, restrainingbars 38 automatically begin to release the edges of sheet 9S as showninF'ig. 5, and such release will be complete when the bending rolls andrestraining bars are positioned as shown in Fig. 6. This feature isillustrated in the schematic Figs. 4, 5, and 6 and will be furtherdescribed in detail.

At the point of the bending operation shown in Fig. 6, the movement ofracks 86 is reversed and rolls 70 and 'l2 are raised. Hold-down plate 44is also raised by operating lever 58. Since the restraining bars 38 willhave automatically released the edges of sheet 96 at or prior to the endof the bending operation, the bent sheet can be easily removed. Eitherbefore or after such removal restraining bars 38 are restored to theposition shown in Fig. 1.

As has been stated above, the edges of sheet 96 are held in restraint bybars 38 during substantially the greater part of the bending cycle, and,when the bending is completed or substantially completed, therestraining bars 38 automatically release the edges of the sheet. Thisunique feature is accomplished by proper positioning of the pivotingpoints 34 about which arms 32 and restraining bars 38 are caused toturn. It has been found that, as sheet 96 is bent to conform to thecurvature 30 of mold 24, the edge of the sheet describes a curve whichcorresponds to substantially the involute of a, part of the circlearound which the sheet is bent. With this knowledge and by graphicallyplotting the curvature of mold 24 and the final curvature of sheetmaterial 93, as illustrated in Fig. 7, point 34 may readily be sodetermined and located that the restraining bars 38 will hold sheetmaterial in restraint by its edges during the critical portion of thebending operation and automatically release the edges at or shortlybefore the end of the bending operation.

Point 34 is located as follows: An arc 98 corresponding to the radius ofcurvature of the desired bend is drawn as shown in Fig. 7. This arccorresponds to curvature 30 of the mold. A second arc I 00 representingthe nal bend in sheet 96 is drawn and is spaced from arc 98 by adistance equal to the thickness of the sheet to be bent. A third are |92representing the center line of the sheet is also drawn. Arc 98 is thensubdivided into relatively small segments, for example degree segments,by the radius lines |04, and such lines extended to intersect arc |02.From the points of intersection between arc |02 and radius lines |04,tangents |96 are projected. On succeeding projected tangents |06, points|08 are established by successively subtracting from distance A to B(distance from point where bending of sheet begins to edge of sheet) thelength of the ,arc from A to the point of intersection between radiuslines |04 and arc |02, and then plotting the difference on thecorresponding tangent line. A series of points |08 are thus establishedon the projected tangents. By connecting points |08 a portion of theinvolute curve |09 described by the edge of board 96 when bent over thecurvature of arc 98 is established.

This involute curve |09 is substantially arcuate for a considerable partof its length, after which it departs inwardly from the arcuate form. Atany two suitable points, as X and Y, near the middle portion of thearcuate part of the involute curve, perpendiculars are drawn to thiscurve, and the point where the perpendiculars intersect represents thepivot point 34. In the bending apparatus, this pivot point 34 isgenerally below the horizontal plane of the sheet 96 as originallyplaced upon mold 24 and is in close proximity to the upper portion ofthe curvature 30 of the mold 24 over which the sheet is bent.

The arms 32 are mounted to pivot about points 34 so determined. In theturning movement of the restraining bars 38 their recessed parts 39describe an arc ||0 as arms 32 are turned about the pivot points 34.This arc ||0 described about point 34 as the center and with the sameradius as that of the arcuate portion of the involute curve |09 willclosely follow the involute curve |09 through an arc of about 50 to 75degrees, which approximately represents the critical sheet bendingrange. Consequently, within this range of travel of bars 38 the sheet 96which is being bent will be restrained by its edges engaging in therecesses 39 in restraining bars 38. After following the arc ||0 througha considerable swing as above described, the involute curve |09 departsinwardly from the arc ||0, and at this point indicated by referencecharacter |4 the sheet edges in departing from the arcuate path andfollowing the involute curve |09 start to withdraw from the recesses 39of bars 38, and such withdrawal is complete shortly thereafter. In thisway the automatic release of the sheet from edge restraint is effectedto take place at or preferably shortly before the completion of thebending operation.

Modications (and variations of the method and apparatus may be employed,and it is to be understood that the invention shall not be limited bythe specific description given herein, but only by the scope of theappended claims.

We claim:

1. Apparatus for bending sheet material which comprises a heated rnoldincluding an upper surface portion and downwardly curved spaced sideforming portions, said upper surface portion adapted to support a sheetwith its side portions extending outwardly beyond said curved sideforming portions of the mold, arms at each end of the mold and pivotedat points in a plane below the upper surface of the mold and adjacent tothe curvature of the side portions thereof, restraining bars havingmeans for engaging the sheet by its edges said bars being adjustablysecured to the outer ends of said arms and positioned in substantiallyparallel alignment to the sides of the mold, and rolls adapted to applydownward pressure to the outwardly-extending portions of the sheet toforce these portions of the sheet and also the restraining bars towardthe sides of the mold.

2. Apparatus as defined in claim 1, and also including clamping meansfor holding the sheet to the upper surface of the mold during thebending operation.

3. Apparatus for bending sheet material, which comprises a heated moldincluding an upper surface portion and a downwardly curved side portion,said upper surface portion adapted to support a sheet with its sideportion extending outwardly beyond the curved side portion of the mold,clamping means for holding the sheet to the upper surface portion of themold, an arm pivoted at each end of the mold, a restraining memberhaving a recessed portion for engaging the sheet by its edge, saidmember being adjustably secured to the outer ends of said arms andpositioned in substantially parallel alignment to the side of the mold,and movable means adapted to apply downward pressure to theoutwardlyextending side portion of the sheet to force the side portionof the sheets and said restraining member toward the side of the mold.

4. Apparatus for bending sheet material which comprises a heated moldincluding an upper surface portion and downwardly curved side portions,said upper surface portion adapted to support a sheet with its sideportions 'extending outwardly beyond said curved side portions of themold, clamping means for holding the sheet to the upper surface portionof the mold, arms pivoted at each end of the mold, a pair of restrainingmembers having recessed portions for engaging the sheet by its oppositeedges, said members being adjustably secured to the outer ends of saidarms and positioned in substantially parallel alignment to the side ofthe mold, and movable means adapted to apply downward pressure to theoutwardly eX- tending side portions of the sheet to force the sideportions of the sheet and said restraining members toward the side ofthe mold.

5. A method of bending sheet material which comprises bending a sheetinto a curvedl formation such that in bending the sheet each of itsedges describes substantially an involute curve, restraining the sheetwhile bending by application 'of inwardly-directed pressure to itsopposite edges and carrying such application to each of the sheet edgesthrough a substantial portion of a substantially arcuate path with whichpath said involute curve is substantially coincident in part and in partdeparts therefrom, and utilizing such departure to effect the release ofthe edges of the sheet from such pressure application.

6. A method according to claim 5, and in which the sheet is clamped atits middle portion during the bending operation.

7. A method according to claim 5, and in which the release defined insaid claim is effected after at least the principal part of the bendinghas been completed.

8. A method according to claim 5, and in which the sheet is clamped atits middle portion during the bending operation and in which the arcuatepath and the involute curve substantially coincide for at least 9. A-method of bending sheet material which comprises applying substantiallyvertical clamping .pressure along an area extending substantiallyparallel to the side edge of the sheet, bending the sheet into a curvedformation such that 'in bending the sheet said side edge describessubstantially an involute curve, restraining the sheet during bendingthereof by application to the saidsfide edge inwardly-directed pressureat substantially right angles to said clamping pressure and carryingsuch application of inwardly-directed pressure through a substantialportion of a substantially arcuate path with which path said involutecurve is substantially coincident in part land in part departs therefromand utilizing such departure to effect the release of the sheet fromsuch inwardly-directed pressure application.

v10. A method according to claim 9, and in which the release defined inYclaim 9 is effected after the principal part of the bending has beencompleted.

1 1. A method according to claim 9, and in which the arcuate path andthe involute curve substantially coincide for at least 50.

ROBERT M. BOEHNL AARON A LADON.

REFERENCES CITED The yfollowing references are of record in the file ofthis patent:

NITED STATES PATENTS

